scripts: Use ${CT_TARGET}-strip to strip gdbserver

Signed-off-by: Zhenqiang Chen <zhenqiang.chen@linaro.org>
[yann.morin.1998@free.fr: quote variables]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Message-Id: <CACgzC7BU9CPZ2cE+EYqnMe2WNz-wYby6f4tsmjJi715WmPmbWw@mail.gmail.com>
PatchWork-Id: 185303

 # Compute Alpha-specific values

 CT_DoArchTupleValues () {

     # The architecture part of the tuple:

     CT_TARGET_ARCH="${CT_ARCH}${CT_ARCH_ALPHA_VARIANT}"

 }